Casing for electrical apparatus



Aug. 5 1924 1.. H. BURNHAM CASING FOR ELECTRICAL APPARATUS Fi led June 8, 1922 r wm w ou t m A 6H .s w H w o UNITED STATES PATENT OFFICE.

LOCKE BURNT-11AM, 0F PIT'ISFIELD. MASSACHUSETTS, ASSIGNOR. TO GENERAL ELECTRIC GQMPANY, GO'RPQRATIGN OF NERV YORK.

CASING ELECTRICAL APPARATUS.

Application filed June 8, 1922.. erial No- 566,918.

To all wizom it may concern:

Be it known that I, Loom. H. UURNHAM, a citizen of the United States, residing at Pittsfield, in the county of Berkshire, Stateof Massachusetts, have invented certain new and useful Improvements in Casings for Electrical ixpparatus, of which the following is a specification.

My invention relates to casings for electrical apparatus, and more particularly, to casings arranged to enclose electrical induction apparatus which is immersed in an in sulating fluid such as oil. The general object of the invention is to provide an improved construction adapted to permit not only the normal'expansion and contraction of the liquid caused by changes in temperature from the heat generated in the immersed apparatus but also to permit without injury to the casing such sudden or rapid expansion as may be caused by short-circuits or other faults which may occur in the apparatus.

Other objects and advantages will appear from the following description taken in connection with the accompanying drawing which shows one embodiment of the invention.

In this particular embodiment of the invention, a casing 1 is adapted to enclose a body of suitable insulating and cooling liquid such as oil in which a transformer or other electrical apparatus is immersed. Heat generated by the immersed apparatus causes variations in the temperature and consequent expansion and contraction of the liquid within the casing 1. An expansion chamber or conservator 2 is connected by a pipe 3 with the lower part of the casing 1, the liquid extending from the casing through the pipe 3 and partially filling the expansion chamber 2 as indicated by the line a. The casing 1 is preferably completely fill d with liquid to exclude all air or other gases which might contaminate it and impair its insulating properties and the level of the liquid in the expansion chamber is preferably slightly higher than that of the liquid in the casing 1 so that a leak at the cover of the casing will not result in air being drawn into the casing.

One of the main features of the invention has to do with the pipe 3. The occurrence of an accidental fault, such as a short circuit or are, within the immersed apparatus may result in the sudden formation of con siderable quantities of heated gases and vapors and cause dangerous pressure within the casing 1 unless some means is provided to prevent such excessive pressure. Such means is provided by the pipe 3 the size of which is such as to permit a rapid flow of liquid, gas and vapor and in this way to prevent excessive pressure Within the casing 1, this being in addition to its normal func tion of permitting a slow movement of liquid back and forth between the casing 1 and the expansion chamber 2, as the liquid Within the casing expands and contracts under the influence of varying temperature. One advantage secured by connecting the large pipe 3 to the lower part of the casing is that any moisture or sediment which may find its way into this pipe from the liquid in the expansion chamber 2 will settle into the bottom of the casing 1 where it can do no harm and without coming into contact with the immersed apparatus. Another advantage is that the coolest liquid in the casing 1 is always in the lower portion thereof and therefore any liquid flowing into the pipe 3 or expansion chamber 2 from the casing is always from the coolest part of the casing. The liquid in the expansion chamber is therefore kept cool and less subject to oxidation or other contamination than if it were heated. If desired, the upper end of the pipe 3 may be extended a short distance above the bottom of the expansion chamber 2 as indicated in the drawing. This will prevent most of the moisture and sediment which may settle in the expansion chamber from passing on through the pipe into the casing.

A small pipe 5 connecting the upper part of the casing 1 with the expansion chamber 2 prevents any accumulation of gas in the casing. This pipe 5 is formed with a depending loop to collect moisture or sediment.

A large pipe or outlet 6 leading from the expansion chamber 2 is normally sealed by a relief diaphragm 7 designed to exclude air, moisture and other undesirable matter from the expansion chamber but to be ruptured by abnormal pressure within tl e expansion chamber and so to relieve such pressure before it reaches dangerous values.

The size of the pipe 3 is determined mainly by the amount of insulating oil in the main casing l ecause the amount of gas formed as the result of a fault in the immersed apparatus depends on the amount of oil from which it is formed. It must be possible for the contents of the casing 1 to escape through the pipe 3 rapidly enough to prevent excessive pressure in the casing and it has been found that in order t function properly as a pressure relief pipe, the cross sectional area of the pipe must be at least one half of one per cent of that of the casing 1. This means that to protect a casing seven in diameter; the diame ter of the pressure relief pipe must be at least six inches. The relief pipe may be and preferably is somewhat larger than this minimum size in order to provide a reasonable factor of safety.

By means of the large pipe 3 and the expansion chamber 2, the invention provic es an emergency path to carry rapid flow of liquid from the lower part of the casing l to a level above the highest part of the liquid within the casing and preferably as in the embodiment of the invention which has been described, this path is unob tructed This prevents possibility of dangerous pressures within the casing. it the same time. this large pipe and expansion chamber permit normal-expansion and contraction of the liquid under the influence of varying temperature and during normal operation of the apparatus only cool liquid can l ave the casing. Furthermore, the body of air or other gas above the liquid in the expan sion chamber provides an effective cushion against which the liquid may expand surldenly from the casingthrough the large pipe without excessive shock.

lVhat I claim as new and desire to secure Letters Patent of the United States,

1. The combination with a casing for inimersed electric induction apparatus, of an expansion chamber, a pipe connecting the expansion chamber to the lower part of said casing, and an insulati liquid within said casing and extending through the pipe into the expansion chamber said pipe having); a cross sectional area at least as great as one half of one per cent of that of said cas ng whereby the pipe may carry a rapid flow of liquid to prevent dangerous pressure within the casing upon the occurrence of a fault in he apparatus.

2. The combination with a casing for immersed electric induction apparatus, of an expansion chamber, a pipe connecting the expansion chamber to the lower part of said casing and an insulating liquid within said casing and extending through the pipe into the expansion chamber to a level above that of the liquid in the casing, said pipe having a cross sectional area at least as great as one half of one per cent of that of said casing. whereby the pipe may carry a rapid flow of liquid to prevent dangerous pressure within the lasing upon the occurreiu-e of a fault in the apparatus.

In witness whereof, I have hereunto set my hand this 6th day of June 1922.

LOCKE H. BURNHAl/l. 

